Method of making fluoboric acid and its compounds



ber heated to a temperature above 600 Patented July 2, 1946 Munro!) OF MAKING FLUOBORIC ACID AND ITS COMPOUNDS Wayne E. White,

County, Pa., assignor of America, Pittsburgh,

Pennsylvania Plum Township, Allegheny to Aluminum Company Pa., a. corporation of No Drawing. Applicationdanuary 17, 1945,

Serial No. 573,318

8' Claims. (01. 23-139) The acid HBF4, commonly called fluoboric acid, has extensive commercial use in many applications which require the use of an acid of high purity. Present methods of manufacturing high purity fiuoboric acid'are expensive and relatively unsatisfactory. The acid is highly corrosive .a'nd noxious, and because of its nature many dimculties are attendant upon its handling; storage and transportation.

This invention provides a new method of manufacture by which fluoboric acid may be rapidly and economically produced in large quantities.

It is a; further advantage of the methods of thisinvention that the acid may be manufactured with use. This latter advantage, coupled with the fact that the material from which the acid is made is relatively non-corrosive, reduces or removes .many of the difficulties and much of the expense heretofore encountered in the handling, storage and transportation of fluoboric acid.

The method of this invention utilizes as a starting material, ammonium fiuoborate (NHlBFn. In accordance with the invention this ammonium salt is heated to cause dissociation thereof and formation ,of gaseous fiuoboric acid, nitrogen and hydrogen. In referring herein to the production of gaseous fluoboric acid in this manner, I mean that gaseous material is produced containing hydrogen fluoride (HF) and boron trifluoride (BFa) values in the ratio required for the formation of fluoboric acid, without regard to whether such values are actually associated as fluoboric acid or as a mixture of separate gaseouscompounds.

The above mentioned heating operation can be effected by first heating the ammonium fluoborate at temperatures above 250? 0., preferably 275-350 C., and by then heating the vapors thus produced, without intermediate cooling, at temperatures in excess of 600 C. Within these limits the time at heat 'for best results is dependent upon the temperature, efliciency being promoted by the use of the higher temperatures. I prefer to operate the second heating step mentioned at about woo-900 C., peratures promote efficiencyv without too much depreciation in the equipment used. The process can be successfully practiced at pheric pressures.

Instead of successive heating operations carried out as described in the preceding paragraph, the heating can be effected by introducing ammon'ium'fluoborate directly into a zone or cham- C., wherein normal atmosa-minimum of equipment at the place of.

having found that such tem-.

and heating ofthe C. occurs. In either dissociation of the fiuoborate resultant vapors at above 600 mode of operation ammonium fluoborate is-heated v at above 250' C., and the vapors formed by dissociationof the ammonium fluoborate are heated at temperatures in excess of 600 C.

The presenceof a catalyst duringheating, such as, for instance, iron or nickel, is advantageous -since the eficiency of the reaction at a given temperature is thereby increased. v

Following such heating operations, the gaseous fluoboric acid produced canbe separated in various ways from the nitrogen and hydrogen mixed therewith. If it is desired to produce an aqueous fluoboric acid solution, the mixture of fiuoboric acid, nitrogen and hydrogen, produced as described above, can be passed into water. The

relatively insoluble nitrogen and hydrogen are not dissolved in the water to any appreciable extent and 'pass 05, leaving a solution of fluoboric acid. In this manner fiuoboric acid solutions can be produced in concentrations as high as -85 per cent of HBFi without difiloulty.

Alternatively, organic solvents of the polar type, such as the alcohols, can be used instead of water to take up the fluoboricacidin a similar manner. In a further alternative. the gaseous fluoboric acid may be caused to react with a material which is relatively inert to the nitrogen and hydrogen present. For example,,the mixed ,vapors can be led into contact with ethanolamine or monoethanolamine, to yield thereby substituted ammonium salts, such as triethanol or monoethanol ammonium fluoborate.

The presence of traces of ammonia in the gaseous mixture produced byv the heating operation at above 600 C., or in the solutions or compounds produced as mentioned above because of ammonia in the vapors. can be substantially eliminated by cooling the vapors to temperatures below about 300 C., and preferably below those at which ammonium fluoborate sublimes.

As an example of the specific operation of my following: A quantity 'of ammonium fluoborate was heated to about 300 C.;

the vapors thus produced were then heated in the presence of steel wool-to a temperature of 800 C. The resulting gaseous products of the reaction were then cooled to about room temperature and, thus cooled, were passed into a quantity of water. Nitrogenand hydrogen were not absorbed in the water and passed oif,.together with'a small proportion of the fluoborlc acid vapor. The opera tion was continued until an. aqueous solution containing '74 per cent by weight of fluoboric acid a liquid amine, such as tri- I was obtained. This available from the aseous mix with a material 75 per cent of the fluoboric acid theoreticallyquantity of ammonium fluoborate processed.

' An outstanding advantage of the processes of this invention resides in the fact that by its use fluoboric acid may be quickly and easily produced from ammonium fluoborate at the point where the acid is to be used. This'results in substantial saving in transportation costand elimination oi serious difiiculties now attendant upon solution contained about 3.The of fluoboric add which comprisesheatmgilnobomte atatemperatureoIatleastwGJieatingthe vaporthusformedatatemperaturedatleast 600 0., subsequentlycooling the gaseous "mixtoatemperaturebelnwmcaandtherethe shipment. of fluoboric acid in commerce.

Fluoboric acid solutions of regular commercial grade contain about 35 to 45 per cent by-weight of HZBFr. Thus relatively large amounts of water must be transported and stored in the shipment of the acid from one point to another. These aqueous solutions must be storedand shipped in rubber-or rubber lined drums. While more concentrated solutions 01' fluoboric acid can be made,

solutions containing more than 50 per cent by weight of fluoboric acid fume at ordinary temperatures and increase handling and shipping dimculties. The use of ammonium fluoborate and its conversion at the time and point of use into fluoboric acid by the simple and" inexpensive advantageous. Moreover, the salt is non-corrosive and non-hygroscopic and may be stored or shipped in more ordinary typesoi containers. With a pure ammonium fluoborate processed in accordance with this invention, yields as high as substantially 100 per cent of the fluoboric acid in the salt can be obtained.

after contacting said mix with; material capable or separating fluoboric acid 4. The process of producing fluoboric acid which comprises heating ammonium fluoborate 'atatemperaturedatleast2500.,heatingthe vapor thus formedat ate-lemme u 4 -ofatleast 600 0., and thereafter the resultant aseousmixwith-amaterialcapalfleot fluoboric acid therefrom by of fluoboric acid.

' methods of this invention are, therefore, highly attemperatureaot250-350" 5.'I'he processotafluobm-macid compound which comprise heating ammonium fluoborat'e at a. temperature of at least 250 0., heating the vapor thus tom-medal; a. temperature of at'1east 600 0., and thereatter thereslfltantmixwithamaterialcapable of separating fluoboric acidthereirmn by reaction with the fluoboric aci 6.The processofproducingafiuohoricacid compound which comprises heating ammonium fluoborate at a temperature 01' at least 250 0., heating the vapor thus iormed at a temperature of at least 600' 0., 'and the resultant gaseous mix with an amine capable of I separting fluoboric acid fllerefrom by reaction with the fluoboric acid.

'7. The processor producing fluoboric acid whichcomprisesheatingammonimnfluobomte' at temperatures of 250-350' 0. and heating the vapor thus formed at a temp r ture of at least 600 0.

at The proces of fluoboric acid which comprises heating ammonium fluoborate 

